1. Field of the Invention
The present invention relates to a mechanism of preventing breakage of a member for suspending a spare wheel in an apparatus for holding a spare wheel to a motor vehicle.
2. Prior Art
1) A spare wheel holding apparatus is provided with a wheel support member for supporting a spare wheel, and a winding device of large reduction ratio for winding up the wheel support member. The wheel support member is connected to the falling end of a suspending member such as a chain or a wire rope of the winding device.
In a large transportation vehicle such as a truck or a middle or small passenger car such as a wagon, as shown in FIG. 3, a winding device of a spare wheel holding apparatus is installed at the lower side of a car body V, and a spare wheel T is wound up and held to the lower surface of the car body V.
In the case that the spare wheel T is held to the lower surface of the car body V, being different from the case that the spare wheel is stored in the car body, when the motor vehicle collides, large forces may be applied to the spare wheel and a large winding-off force may be applied to the suspending member of the winding device.
When the large winding-off force is applied to the suspending member of the winding device, since the winding device has large reduction ratio, the suspending member is not wound off and is broken. If the suspending member is broken, the spare wheel and the wheel support member are separated from the car body and run with inertia on a road and may collide with a walker, other motor vehicle or the like, resulting in dangerous state.
2) The present inventor has invented a spare wheel holding apparatus for preventing breakage of a suspending member of a winding device, as disclosed in JP-B 2768661.
In the spare wheel holding apparatus, a winding device is constituted by a case having vertical cross-section in nearly portal shape, and a main shaft is supported to a front side plate and a rear side plate of the case, and a winding drum on which a suspending member is to be wound is fitted rotatable to the main shaft, and a planetary gear mechanism having large reduction ratio is provided.
The planetary gear mechanism is constituted in that an internal gear is provided concentrically to the side surface of the winding drum, an eccentric cam is provided on the main shaft, an external gear is fitted rotatable to the eccentric cam, the internal gear and the external gear are meshed with each other in relation of the inside and the outside, and a rotation restricting plate is fixed to the side surface of the external gear so that the left end or the right end of the rotation restricting plate abuts on the top plate of the case thereby the rotation is restricted. When the winding-off force is applied to the suspending member, the right end of the rotation restricting plate abuts on the top plate of the case.
The right end of the rotation restricting plate is made desired weak strength. If the winding-off force applied to the suspending member is larger than that during normal use, the weak right end of the rotation restricting plate is broken, and the winding drum is rotated reversely and the suspending member is wound off thereby the breakage of the suspending member is prevented.
In such a spare wheel holding apparatus where breakage of a suspending member of a winding device is prevented, on the occasion that large winding-off force is applied to the suspending member by the collision of a motor vehicle and a rotation restricting plate is broken at the weak right end and a winding drum is rotated reversely and the winding member is wound off, when the winding drum is rotated reversely by turn of about three-fourths, the strong left end of the rotation restricting plate abuts on the top plate of the case, and the reverse rotation of the winding drum is stopped and the suspending member is no more wound off.
If the large winding-off force is applied to the suspending member even after the strong left end of the rotation restricting plate abuts on the top plate of the case and the reverse rotation of the winding drum is stopped, the suspending member is not wound off and will be broken. In the case that large winding-off force is applied to the suspending member continuously or intermittently for a long time, it is difficult to prevent the breakage of the suspending member securely.
In the weak right end of the rotation restricting plate, in order to set the strength to a desired value, thickness or shape is adjusted. However, when the thickness of the rotation restricting plate is adjusted, the range of increasing or decreasing the thickness is narrow. Also when the shape of the rotation restricting plate is adjusted, in order to correct a punch and a die for blanking the rotation restricting plate much labor is required.
Setting of the strength in the weak right end of the rotation restricting plate is not easy. Setting of the winding-off force for the suspending member of the winding device to start the winding-off is difficult.
Even if the winding-off force applied to the suspending member is the same, the weak right end of the rotation restricting plate may be broken or may not be broken depending on the position of the eccentric cam. In other words, the winding-off force of the suspending member that the weak right end of the rotation restricting plate is broken is different depending on the position of the eccentric cam. Consequently it is very difficult that the weak right end of the rotation restricting plate is always broken and the winding drum is rotated reversely when the winding-off force applied to the suspending member becomes a definite value or more.
In order to clarify the reason, the state that the winding-off force is applied to the suspending member will be considered from the standpoint of mechanics.
As shown in FIG. 6(a), if winding-off force W is applied to a suspending member 8, winding-off, moment Wxc2x7a will be generated about the rotation center axis of the main shaft 3, where xe2x80x9caxe2x80x9d is a definite value and means distance between the winding-off force W and the rotation center axis of the main shaft 3, i.e., the length of the arm of the winding-off moment.
In FIG. 6(a), by the winding-off moment Wxc2x7a in the counterclockwise direction, a winding drum 6 and an internal gear as one body, an external gear and a rotation restricting plate 31 as one body, and a main shaft 3 and an eccentric cam 9 as one body are subjected to the rotational force in the counterclockwise direction, and the weak right end 32 of the rotation restricting plate 31 abuts on a top plate of the case 2. The right end 32 of the rotation restricting plate 31 is subjected to reaction force from the contact point position of the top plate of the case 2 with the right end 32. Then by the reaction force, moment in the clockwise direction about the rotation center axis of the main shaft 3 is generated in the external gear and the rotation restricting plate 31 as one body, the winding drum 6 and the internal gear as one body, and the main shaft 3 and the eccentric cam 9 as one body. The moment in the clockwise direction by the reaction force balances with the winding-off moment Wxc2x7a in the counterclockwise direction.
As shown in FIG. 6(a), when the center of the eccentric cam 9 is positioned at the right upper side of the rotation center axis of the main shaft 3 and gets near the contact point of the right end of the rotation restricting plate 31 with the top plate of the case 2, the distance between the contact point and the rotation center axis of the main shaft 3 becomes L1. The distance L1 is the length of the arm of the clockwise moment by the reaction force R1. The clockwise moment R1xc2x7L1 by the reaction force R1 balances with the counterclockwise winding-off moment Wxc2x7a.
On the contrary, as shown in FIG. 6(b), when the center of the eccentric cam 9 is positioned at the left lower side of the rotation center axis of the main shaft 3 and gets away from the contact point of the right end 32 of the rotation restricting plate 31 with the top plate of the case 2, the distance between the contact point and the rotation center axis of the main shaft 3, that is, the length: of the arm of the clockwise moment by the reaction force R2 becomes L2. The clockwise moment R1xc2x7L2 by the reaction force R2 balances with the counterclockwise winding-off moment Wxc2x7a.
The arm length L1 in the former and the arm length L2 in the latter are different by about two times of the eccentric distance between the eccentric cam 9 and the main shaft 3. Consequently assuming that the clockwise moment R1xc2x7L1 by the reaction force R1 and the clockwise moment R1xc2x7L2 by the reaction force R2 balance with the same counterclockwise winding-off moment Wxc2x7a and become the same value, since the arm length L1 and the arm length L2 of the moment are different, difference is produced in the amount of the force of the moment and in the amount of the reaction force R1 and the reaction force R2.
As a result, even if the winding-off force W applied to the suspending member 8 is the same, depending on the position of the eccentric cam 9, the reaction force R1 and the reaction force R2 to bend the right end 32 of the rotation restricting plate 31 to the right lower side are different in amount, and the right end 32 of the rotation restricting plate 31 may be broken or may not be broken.
In a spare wheel holding apparatus where when a winding-off force larger than that in normal use state is applied to a suspending member of a winding device, the suspending member of the winding device is wound off thereby breakage of the suspending member is prevented, a first object of the present invention is to provide a suspending member breakage preventing mechanism where even if a winding-off force larger than that in normal use state is applied to a suspending member for a long time, breakage of the suspending member is prevented.
In the above-mentioned spare wheel holding apparatus, a second object of the present invention is to provide a suspending member breakage preventing mechanism where a winding-off force for the suspending member of the winding device to start the winding-off can be easily set.
In the above-mentioned spare wheel holding apparatus, a third object of the present invention is to provide a suspending member breakage preventing mechanism where when a winding-off force applied to the suspending member becomes nearly a constant value or more, breakage of the suspending member is always prevented.
The present invention is as follows.
1) A suspending member breakage preventing mechanism in a spare wheel holding apparatus,
wherein the spare wheel holding apparatus is provided with a wheel support member on which a spare wheel is supported, and a winding device having a suspending member which connects the wheel support member to the falling end of the suspending member,
the winding device is provided with a case, a main shaft supported on the case, a winding drum for winding the suspending member, said drum being rotatably fitted to the main shaft, and a planetary gear mechanism having large reduction ratio,
the planetary gear mechanism is constituted in that an internal gear is provided concentrically on the side surface of the winding drum, and an eccentric cam is provided on the main shaft, and an external gear is rotatably fitted to the eccentric cam, and the internal gear and the external gear in eccentricity are meshed in relation of the inside and the outside, and a rotation restricting plate is provided to the side surface of the external gear, and a rotation restricting pin is provided on the case so that the rotation restricting plate abuts on the rotation restricting pin and the rotation of the external gear on its own axis is restricted,
the rotation restricting pin serves also as a safety pin where the strength is set so that when a winding-off force is applied to the suspending member, the rotation restricting plate abuts on the rotation restricting pin, and when the winding-off force applied to the suspending member is larger than that at the normal use state, the rotation restricting pin is broken, and
when the rotation restricting pin serving also as the safety pin is broken, the winding drum can be rotated reversely by one turn or more, and the suspending member is wound off thereby the breakage of the suspending member is prevented.
2) In the above-mentioned suspending member breakage preventing mechanism, when a winding-off force is applied to the suspending member of the winding device, distance between the contact point of the rotation restricting plate abutting on the rotation restricting pin serving also as the safety pin and the rotation center axis of the main shaft is substantially constant irrespective of the position of the eccentric cam.
3) In the above-mentioned suspending member breakage preventing mechanism, the rotation restricting plate is provided with a groove in the direction from the circumferential surface toward the eccentric cam, and the rotation restricting pin serving also as the safety pin is inserted in the groove.
4) In the above-mentioned suspending member breakage preventing mechanism, the case of the winding device is fixed to a car body of a motor vehicle, and the spare wheel supported on the wheel support member is wound up and held to the lower surface of the car body.
When large force is applied to a spare wheel supported on a wheel support member by collision of a motor vehicle, and a winding-off force larger than that in normal use state is applied to a suspending member of a winding device, in the winding device, a rotation restricting pin serving also as a safety pin abutting on a rotation restricting plate is broken and a winding drum is rotated reversely and the suspending member is wound off thereby breakage of the suspending member is prevented. When the rotation restricting pin serving also as the safety pin is broken, since the winding drum can be rotated reversely by one turn or more, even if the large winding-off force is applied to the suspending member continuously or intermittently for a long time, breakage of the suspending member is prevented.
In the rotation restricting pin serving also as the safety pin, the strength can be set to a desired value by adjusting diameter and the setting of the strength is easy. The setting of the winding-off force for the suspending member of the winding device to start the winding-off by the breakage of the rotation restricting pin serving also as the safety pin is easy.
When the winding-off force is applied to the suspending member of the winding device, since distance between the contact point of the rotation restricting plate abutting on the rotation restricting pin serving also as the safety pin and the rotation center axis of the main shaft becomes substantially constant irrespective of the position of the eccentric cam, the winding-off force of the suspending member for the rotation restricting pin serving also as the safety pin to be broken is scarcely varied by the position of the eccentric cam and becomes substantially constant value. When the winding-off force applied to the suspending member becomes substantially constant value or more, the rotation restricting pin serving also as the safety pin is always broken and the winding drum is rotated reversely and the breakage of the suspending member is prevented.